Thermally adhesive sheath-core conjugate fiber and tricot fabric

ABSTRACT

A thermally adhesive sheath-core conjugate fiber has, as a core part, a polyester having a melting point of at least 250° C., and has, as a sheath part, a polyester having a melting point which is at least 215° C. and is 20-35° C. lower than the melting point of the polyester constituting the core part. The thermally adhesive sheath-core conjugate fiber is characterized by having a strength of 3.8 cN/dtex or higher and an elongation of 35% or higher.

TECHNICAL FIELD

This disclosure relates to a thermally adhesive sheath-core conjugatefiber having low fuzz generation in a high-order process, exhibitsexcellent high-order passability even in uses such as tricot use and thelike, requiring a high quality level, enables a woven or knitted fabrichaving excellent strength, dimensional stability, and durability afterthermal adhesion, and having an excellent quality level as a flow pathmaterial of a liquid filtration membrane.

BACKGROUND

A polyester fiber is suitable as a raw material fiber for clothing andindustrial materials and the like due to its excellent dimensionalstability, weather resistance, mechanical properties, durability, andproductivity that can be mass-produced relatively inexpensively and thelike, and used in various fields and uses.

In recent years, in material uses such as a flow path material for awater treatment membrane and a filter, interior uses such as a chair anda partition, and other various clothing uses, utilization of a thermallyadhesive polyester fiber capable of improving the form retention andrigidity of a fabric proceeds. The thermally adhesive polyester fiber isobtained by forming a polyester fiber into a woven or knitted fabric,and then subjecting the fabric to a heat treatment such as calenderingto partially melting fibers, thereby thermally adhering the fibers.Above all, the demand for a water treatment membrane increases year byyear to mainly solve serious water shortage caused by a populationincrease in the Middle East and Africa regions. In a member serving as aflow path of permeation water filtered in a water treatment device, thedemand for a polyester tricot flow path material obtained by thermallyadhering a polyester tricot fabric rapidly increases.

As the thermally adhesive polyester fiber, a yarn composed of 2 or moretypes of polyesters having different melting points or softening pointsis suitable. Examples include a mixed fiber including a filament yarn,and a sheath-core type or side-by-side type conjugate fiber. A conjugatefiber in which a filament single yarn includes polymers having differentmelting points has an excellent quality level after thermal adhesioncompared to a mixed yarn in which filaments having different meltingpoints are mixed at a single yarn level. In particular, a thermallyadhesive sheath-core conjugate fiber is actively used. The thermallyadhesive sheath-core conjugate fiber is a sheath-core conjugate yarnhaving an excellent quality level such as productivity of an originalyarn or surface smoothness of a fabric after a heat treatment, wherein asheath component has a melting point or a softening point lower thanthat of a core component.

A sheath-core conjugate fiber including a core part including apolyester whose main repeating unit includes ethylene terephthalate anda sheath part including a polymer having a softening temperature of 130to 200° C. has been proposed as the thermally adhesive sheath-coreconjugate fiber in Japanese Patent Laid-Open Publication No. 62-184119.

The above-mentioned sheath-core conjugate fiber makes it possible toprovide a high-quality thermally adhesive woven or knitted fabric havingpredetermined strength and elongation characteristics without causingoccurrence of yarn slippage and embossing due to slippage at a thermaladhesion intersection. However, as exemplified by a polyester obtainedby copolymerizing isophthalic acid as a preferred composition of apolymer used for a sheath component, the polymer of the sheath part haslow crystallinity which does not have a clear melting point. For thisreason, when the woven or knitted fabric made of the sheath-coreconjugate fiber is subjected to a thermal adhesion treatment, unevennessoccurs in adhesion between the conjugate fibers. This causes dimensionalstability and variation in the strength and elongation of the fabric,which disadvantageously causes a poor quality level when used as a flowpath material of a liquid filtration membrane.

Meanwhile, a sheath-core conjugate fiber has been proposed in JapanesePatent Laid-Open Publication No. 2000-119918. The sheath-core conjugatefiber includes a core part including a polymer whose 90% by mole or moreof repeating units include ethylene terephthalate and a sheath partincluding copolymerized polybutylene terephthalate whose 60 to 90% bymole of repeating units include butylene terephthalate.

In the above-mentioned sheath-core conjugate fiber, appropriatecrystallinity is imparted to the sheath component, and the sheath-coreconjugate fiber has good fiber physical properties such as a boilingwater contraction ratio and a peak temperature of heat contractionstress, whereby a thermally adhered woven or knitted fabric producthaving a good quality level can be obtained.

A tricot fabric using a thermally adhesive sheath-core conjugate fiberdescribed in Japanese Patent Laid-Open Publication Nos. 2011-245454 or2014-070279 has also been reported. In those techniques, a polyester isused, which includes a sheath component having a melting pointsignificantly lower than that of a high melting point polyester of acore component. When a spinning temperature is set based only on themelting point of the core component polyester, the heat deterioration ofthe sheath component is apt to proceed. Meanwhile, when the spinningtemperature is lowered in consideration of the melting point of thesheath component polyester, the strength and elongation characteristicsof the core component cannot be maximized so that the conjugate fiberhas a poor strength and elongation.

Since the sheath-core conjugate fiber described in JP '918 has a poorstrength and elongation, the sheath-core conjugate fiber is processed ata high tension and a high speed, which disadvantageously makes itdifficult to develop the sheath-core conjugate fiber into a tricot usein which quality defects of an original yarn such as fuzz notably appearas defects of a fabric. Since the melting point of the sheath componentis low, a thermal adhesion temperature after weaving cannot be increasedso that the contraction of the conjugate fiber constituting the fabricbecomes insufficient. In uses such as a water treatment membrane flowpath material in which high dimensional accuracy is required indesigning the fabric, there is a problem in dimensional stability whenused for a long time under a high pressure. The thermally adhesivesheath-core conjugate fibers described in JP '454 and JP '279 have apoor strength and elongation so that the thermally adhesive sheath-coreconjugate fibers disadvantageously have not only low high-orderpassability, but also an insufficient strength and elongation of thefabric to be formed, which disadvantageously causes poor durability whenused as the flow path material for a long time. For the same reason asthat in JP '918, the thermal adhesion temperature after weaving cannotbe increased so that the contraction of the fibers constituting thefabric becomes insufficient. In uses such as a water treatment membraneflow path material in which high dimensional accuracy is required indesigning the fabric, there remains a problem in dimensional stabilitywhen used for a long time under a high pressure.

It could therefore be helpful to provide a thermally adhesivesheath-core conjugate fiber having low fuzz generation in a high-orderprocess, exhibits excellent high-order passability even in uses such astricot use and the like, requiring a high quality level, enables a wovenor knitted fabric having excellent strength, dimensional stability, anddurability after thermal adhesion, and having an excellent quality levelas a flow path material of a liquid filtration membrane.

SUMMARY

We thus provide:

-   (1) A thermally adhesive sheath-core conjugate fiber including: a    core part which includes a polyester having a melting point of    250° C. or higher; and a sheath part which includes a polyester    having a melting point of 215° C. or higher and lower by 20 to    35° C. than that of the polyester constituting the core part,    wherein the thermally adhesive sheath-core conjugate fiber has a    strength of 3.8 cN/dtex or more and an elongation of 35% or more.-   (2) The thermally adhesive sheath-core conjugate fiber according to    (1), wherein the sheath-core conjugate fiber has a total fineness of    30 dtex or more and a single yarn fineness of 3.0 dtex or less.-   (3) A tricot fabric including the thermally adhesive sheath-core    conjugate fiber according to (1) or (2).

We provide a thermally adhesive sheath-core conjugate fiber having lowfuzz generation in a high-order process, exhibits excellent high-orderpassability even in uses such as tricot use and the like, requiring ahigh quality level, enables a woven or knitted fabric having excellentstrength, dimensional stability, and durability after thermal adhesion,and having an excellent quality level as a flow path material of aliquid filtration membrane.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of the cross-sectional shape of a single yarn ofa thermally adhesive sheath-core conjugate fiber.

FIG. 2 shows an example of the cross-sectional shape of a single yarn ofa thermally adhesive sheath-core conjugate fiber, and is a diagram fordescribing a cross-sectional eccentricity ratio.

DESCRIPTION OF REFERENCE SIGNS

-   1: Core component-   2: Sheath component-   3: Position of center of gravity of core component-   4: Position of center of gravity of conjugate fiber-   5: Radius of conjugate fiber-   10: Thermally adhesive sheath-core conjugate fiber

DETAILED DESCRIPTION

Hereinafter, a thermally adhesive sheath-core conjugate fiber will bedescribed in detail.

A sheath-core conjugate fiber includes a core component including apolyester having a melting point of 250° C. or higher, and a sheathcomponent including a polyester having a melting point of 215° C. orhigher and lower by 20 to 35° C. than the melting point of the polyesterconstituting a core part.

By setting the melting point of the core component polyester to 250° C.or higher, a spinning temperature can be increased to such an extentthat the strength and elongation characteristics of the polyester can bemaximized, which provides an excellent strength and durability of afabric to be formed. The melting point of the core component polyesteris preferably 270° C. or lower from the practical upper limit. When themelting point of the core component polyester is 270° C. or lower, theneed for extremely high temperature spinning is avoided to enablespinning to be performed using a general-purpose melt spinning device,which is preferable. More preferably, the melting point is 253° C. orhigher and 260° C. or lower.

The melting point of the sheath component polyester is 215° C. orhigher, and preferably 250° C. or lower. When the sheath componentpolyester has a melting point of 250° C. or lower, a versatile devicecan be used to thermally adhere the fabric, and smoking caused by an oilagent component in a thermal adhesion treatment can be suppressed, whichis preferable. More preferably, the melting point is 220° C. or higherand 235° C. or lower. By setting a melting point difference between thesheath component polyester and the core component polyester to 20° C. orhigher, the thermal adhesion temperature of the fabric can be madesufficiently lower than the melting point of the core componentpolyester, whereby a highly durable fabric utilizing the strength of anoriginal yarn can be provided. By setting the melting point differenceto 35° C. or lower, the spinning temperature can be set to a temperaturethat maximizes the strength and elongation of the core componentpolyester and suppresses the thermal deterioration of the sheathcomponent polyester as much as possible, whereby a conjugate fiberhaving an excellent strength and elongation, less original yarn fuzz,and an excellent quality level is provided. The melting point differencebetween the sheath component polyester and the core component polyesteris preferably 23° C. or higher and 30° C. or lower.

The softening temperature of the core component polyester is preferably245° C. or higher, and the softening temperature of the sheath componentpolyester is preferably 205° C. or higher. The softening temperature ofthe core component polyester is 245° C. or higher, whereby thedimensional change of the fabric is less, and the form of the fabric isstable when the fabric is subjected to a thermal adhesion treatment at atemperature equal to or higher than the melting point of the sheathcomponent polyester, which is preferable. The softening temperature ofthe core component polyester is more preferably 250° C. or higher. Theupper limit of the softening temperature of the core component polyesteris practically 270° C.

When the softening temperature of the sheath component polyester is 205°C. or higher, high-speed passability is stabilized without causingfusion of the conjugate fiber to a heater during thermal setting in aprocessing step, which is preferable. The softening temperature of thesheath component polyester is more preferably 215° C. or higher. Bysetting the melting point of the sheath component polyester to 215° C.or higher, and setting the softening point to 205° C. or higher, thethermal adhesion temperature of the fabric to be formed can besufficiently increased, whereby the thermal adhesion treatment causesthe thermal contraction of the sheath-core conjugate fiber to proceed toimprove the dimensional stability of a final product, which ispreferable. The upper limit temperature of the softening temperature ofthe sheath component polyester is practically 250° C.

As the core component polyester, optional polyesters can be selected aslong as the melting point is within the above range, but the corecomponent polyester is preferably polyethylene terephthalate(hereinafter, referred to as PET) from the viewpoint of dimensionalstability and strength and elongation characteristics. The PET is apolyester obtained by using terephthalic acid as a main acid componentand ethylene glycol as a main glycol component. The core componentpolyester may appropriately include a copolymerization component as longas the melting point is within the range described above. Examples ofcompounds copolymerizable with, for example, PET include dicarboxylicacids such as isophthalic acid, succinic acid, cyclohexanedicarboxylicacid, adipic acid, dimeric acid, sebacic acid, and 5-sodiumsulfoisophthalic acid, and diols such as ethylene glycol, diethyleneglycol, 2,2-dimethyl-1,3-propanediol, butanediol, neopentyl glycol,cyclohexane dimethanol, polyethylene glycol, polypropylene glycol, andbisphenol A ethylene oxide adduct. It is more preferable that 100% ofthe compound is homo PET including repeating units of ethyleneterephthalate from the viewpoint of dimension stability and strength andelongation characteristics. If necessary, inorganic fine particles madeof titanium dioxide and the like as a matting agent, and silica fineparticles and the like as a lubricant may be added.

As the sheath component polyester, optional polyesters can be selectedas long as the melting point is within the above-mentioned range. Inaddition to PET, polytrimethylene terephthalate and polybutyleneterephthalate are preferable. When the PET is used as the core componentpolyester, the PET is particularly preferably used as the sheathcomponent polyester, in consideration of the peeling suppression of acomposite interface. As the sheath component polyester, an optionalcopolymerization component can be added at an optional ratio as long asthe melting point is within the above-mentioned range. When 70% by moleor more of copolymerized PET includes repeating units of ethyleneterephthalate, moderate crystallinity can be imparted to a polymer, toprovide stabilized spinning operability, which is preferable. When thefabric is subjected to thermal adhesion, thermal adhesion unevenness isless likely to occur, which is preferable. It is more preferable that80% by mole or more of copolymerized PET includes repeating units ofethylene terephthalate. When a polymer other than PET is used as thesheath component polyester, a copolymerization component can beappropriately added as long as original yarn productivity and thequality level of the fabric after a thermal adhesion treatment are notimpaired. As the copolymerization component, optional components such asthe above-mentioned copolymerization component can be copolymerized.Regardless of the type of a polymer selected, if necessary, inorganicfine particles made of titanium dioxide and the like as a matting agent,and silica fine particles and the like as a lubricant may be added.

Next, the intrinsic viscosity (hereinafter, referred to as IV) of theconjugate fiber is preferably 0.55 to 0.75. When IV is 0.55 or more, thetoughness of the conjugate fiber sufficient for withstanding practicaluse can be achieved without a degree of polymerization being too low,which is preferable. Meanwhile, when IV is 0.75 or less, IV is not toohigh during spinning. This makes it possible to suppress an increase inthe amount of COOH during melt spinning without making it necessary toperform extreme high temperature spinning, and provide a uniformconjugate fiber without causing melt fracture, and causes no decrease inthe toughness, which is preferable. More preferably, IV is 0.60 to 0.70.

FIG. 1 is a schematic cross-sectional view of a sheath-core conjugatefiber. In a sheath-core conjugate fiber 10, a core component 1 issurrounded by a sheath component 2.

The cross-sectional shape of the conjugate fiber is not particularlylimited as long as a high melting point component is disposed in a corepart and a low melting point component is disposed in a sheath form tocover the core part, but it is preferable that the sheath componentcompletely covers the core component without exposing the corecomponent. The eccentricity ratio of the center of gravity of the corecomponent with respect to the center of gravity of the entire conjugatefiber is preferably 5% or less in the cross section of the conjugatefiber because of the productivity of the original yarn and the stabilityof physical properties such as Uster unevenness U %. When theeccentricity ratio is 5% or less, coiled crimp is not expressed even ifthe combination of the polymers of the core component and the sheathcomponent is a combination which causes a difference in contraction,which preferably provides an excellent quality level of the fabric. Morepreferably, the eccentricity ratio is 1% or less.

The cross-sectional outer peripheral shape of the conjugate fiber ispreferably a substantially circular shape with a flat ratio representedby AB and being 1.1 or less, where A is a major axis of an outerperipheral shape and B is a minor axis thereof. Such a shape canuniformly disperse and receive a force when an external tension isapplied, and provides also less variation in strength and elongation inthe S-S curve of the conjugate fiber, which is preferable. Morepreferably, the flat ratio is 1.0.

The composite ratio of the core component and the sheath component inthe sheath-core conjugate fiber is set such that the cross-sectionalarea ratio (core:sheath) is preferably 40:60 to 90:10, and morepreferably 55:45 to 75:25. By setting the composite ratio to be withinthe above range, the conjugate fiber can be stably produced, has anexcellent strength and elongation, has low fuzz generation, and canmaintain a strength and an elongation even during thermal adhesion ofthe fabric, which is preferable.

The content of inorganic particles included in the core component is3.0% by weight or less, to improve the toughness, which is preferable.The content is more preferably 0.5% by weight or less. The content ofinorganic fine particles included in the sheath component is 0.05% byweight or more, to improve the process passability, which is preferable.More preferably, the content of the inorganic fine particles included inthe sheath component is 0.05% by weight or more and 0.5% by weight orless because a guide is not excessively abraded during process passing,and unnecessary falling of the inorganic particles when the conjugatefiber is used as a flow path material is not caused. The inorganic fineparticles are preferably made of titanium oxide from the viewpoint ofthe process passability as the conjugate fiber.

The conjugate fiber preferably has a total fineness of 30 dtex or more.By setting the total fineness to 30 dtex or more, a sufficient strengthand rigidity can be ensured by a thermal adhesion treatment. When theconjugate fiber is used as the flow path material, a sufficient passingamount of a permeation liquid can be secured even if a water pressureacts. The total fineness is preferably 90 dtex or less, and morepreferably 40 dtex or more. By setting the total fineness to 90 dtex orless, the thinning of the fabric can be achieved. When the conjugatefiber is used as the flow path material, the number of laminated layersper unit formed by bonding the filtration membrane and the flow pathmaterial can be increased, which is preferable.

The single yarn fineness of the conjugate fiber is preferably 3.0 dtexor less. By setting the single yarn fineness to 3.0 dtex or less, thespecific surface area is increased. This can cause even a short timethermal adhesion treatment to provide uniform thermal adhesion, andprovide a suppressed decrease in the strength of the fabric due to thethermal adhesion treatment, whereby the fabric having high durabilitycan be obtained. The single yarn fineness is preferably 0.7 dtex ormore, and more preferably 1.5 dtex or more and 2.5 dtex or less. Bysetting the single yarn fineness to 0.7 dtex or more, less yarnunevenness and original yarn fuzz are provided, which enables stableproduction, and knitting yarn breakage is less, which provides excellenthigh-order passability, and appropriate rigidity of the fabric to beformed, which is preferable.

The conjugate fiber has a strength of 3.8 cN/dtex or more and anelongation of 35% or more. By setting the strength to 3.8 cN/dtex ormore, a fabric to be formed has a high strength. The fabric hasexcellent durability when the fabric is used as a flow path material.The practical upper limit of the strength is 7.0 cN/dtex. By setting theelongation to 35% or more, the fuzz of the original yarn can beprevented, and the fabric has less warping fuzz during weaving, and lessyarn breakage during knitting, excellent high-order passability, and anexcellent quality level with few defects. The elongation is morepreferably 35 to 50%. A woven or knitted fabric obtained by setting theelongation to 50% or less has excellent dimensional stability, which ispreferable.

To obtain a highly uniform fabric, Uster unevenness U % which is anindex of thickness unevenness in the fiber longitudinal direction of theconjugate fiber is preferably set to 1.4% or less. When the Usterunevenness U % is 1.4% or less, the surface of the fabric after thermaladhesion becomes smooth, and a uniform flow path can be formed when thefabric is used as the flow path material, which is preferable. Morepreferably, the Uster unevenness U % is 1.0% or less.

The dry-heat contraction ratio of the conjugate fiber is preferably 20%or less. By setting the dry-heat contraction ratio to 20% or less, adimensional change due to a thermal adhesion treatment can besuppressed, which is preferable. The practical lower limit of thedry-heat contraction ratio is 2.0%.

A preferred yarn production method will be described. As a spinneretused for a melt spinning method of a thermally adhesive sheath-coreconjugate fiber, an existing composite spinning spinneret can be used.

Examples of the melting method include a pressure melter method and anextruder method, but melting provided by an extruder is preferable fromthe viewpoint of efficiency and suppression of decomposition. A meltingtemperature is preferably set to be higher by 10 to 40° C. than themelting point of a polymer to be used.

The spinning temperature is preferably 280 to 295° C. More preferably,the spinning temperature is 285° C. to 293° C. By employing such aspinning temperature, a conjugate fiber having a high toughness and goodyarn producing properties can be obtained. A heater may be providedbelow a spinneret to alleviate rapid cooling immediately below thespinneret.

By shortening a melting passage time and a heating time from melting todischarging as much as possible, a decrease in the molecular weight ofeach of the core component and the sheath component can be suppressed,which is preferable. The core component and the sheath component areseparately melt-kneaded, precisely discharged and measured through aheating zone, passed through a filter layer for trapping extraneousmatters, and discharged, stringed, and cooled using a compositespinneret to provide a sheath-core form. When a polymer residence timewhich is a passage time from melting to discharging is within 30minutes, the thermal deterioration of the polymer can be reduced, and adecrease in IV is suppressed, whereby a decrease in the toughness of theyarn can be prevented. An increase in the amount of COOH in theconjugate fiber can be suppressed, whereby suppressed fuzz, excellentheat resistance, excellent high-order passability, and improveddurability of the fabric to be formed can be provided, which ispreferable. More preferably, the polymer residence time is 20 minutes orless.

A spinneret surface temperature is preferably set to 270° C. or higherand 290° C. or lower from the balance between the strength andelongation and the productivity. By setting the spinneret surfacetemperature to 270° C. or higher, the characteristics of the corecomponent can be maximized, whereby a yarn having an excellent strengthand elongation can be obtained. By setting the spinneret surfacetemperature to 290° C. or lower, an increase in yarn breakage due to thedeposition of a polymer hydrolyzate immediately below the spinneret issuppressed, which provides excellent original yarn productivity, whichis preferable.

The sheath-core conjugate fiber can be manufactured by any of a two-stepmethod in which a discharged polymer is once wound up as an undrawn yarnand then drawn, and a one-step method such as a direct spinning drawingmethod in which spinning and drawing steps are continuously performed,or a high speed yarn producing method.

A stretching temperature is preferably 60° C. or higher and 100° C. orlower, which is near the glass transition temperature of the undrawnyarn. By setting the stretching temperature to 60° C. or higher, uniformstretching can be provided, and by setting the stretching temperature to100° C. or lower, deterioration in productivity due to fusion of fibersto a stretching roll or spontaneous extension of the fibers can beprevented. More preferably, the stretching temperature is 75° C. orhigher and 95° C. or lower.

It is preferable that the fiber is thermally set at a temperature whichthe crystallization rate of the undrawn yarn becomes the largest afterstretching. The temperature is preferably set to 110° C. or higher and180° C. or lower. The thermal setting at 110° C. or higher makes itpossible not only to promote the crystallization of the fiber toincrease the strength but also to stabilize various kinds of yarnphysical properties including contraction stress and a dry-heatcontraction ratio, which is preferable. The thermal setting at 180° C.or lower makes it possible to prevent deterioration in productivity dueto the fusion of the conjugate fiber to a thermal setting device, whichis preferable.

EXAMPLES

Hereinafter, our fibers and fabrics will be specifically described byway of Examples. Main measured values of Examples were measured by thefollowing methods.

(1) Intrinsic Viscosity (IV)

In the definition formula ηr, a relative viscosity ηr is obtainedaccording to the following formula by dissolving 0.8 g of a sample in 10mL of O-chlorophenol (OCP) having a purity of 98% or more, and using anOstwald viscometer at 25° C., to calculate an intrinsic viscosity (IV).

ηr=η/η0=(t×d)/(t0×d0)

Intrinsic viscosity (IV)=0.0242ηr+0.2634

[η: viscosity of polymer solution, η0: viscosity of OCP, t: drop time ofsolution (sec), d: density of solution (g/cm³), t0: drop time of OCP(sec), d0: density of OCP (g/cm³)].

(2) Melting Point

10 mg of a dried sample was weighed by using a differential scanningcalorimetry (DSC) Q100 manufactured by TA Instruments, sealed in analuminum pan, and then measured at a heating rate of 16° C./min fromroom temperature to 300° C. under a nitrogen atmosphere. After firstmeasurement (1st run), the sample was held for 5 minutes and thenrapidly cooled to room temperature. Second measurement (2nd run) wascontinuously performed, and the peak top temperature of a melting peakin the 2nd run was taken as a melting point.

(3) Softening Temperature

A dried sample was placed on a sample stage by using a thermalmechanical device (TMA/SS-6000) manufactured by Seiko Instruments Inc.,and measured at a heating rate of 16° C./min from room temperature to300° C. under a nitrogen atmosphere using a needle probe having a tipdiameter of 1.0 mm in a state where a measurement load was set to 10 g.A temperature at the start of displacement was taken as a softeningtemperature.

(4) Cross-Sectional Eccentricity Ratio

The cross section of a fiber was observed by using a microscope VHX-2000manufactured by Keyence Corporation, and each value was measured with anattached image analysis software. When the position of center of gravityof a core component was taken as C1 (numeral number 3 in FIG. 2); theposition of center of gravity of a conjugate fiber was taken as Cf(numeral number 4 in FIG. 2); and the radius of the conjugate fiber wastaken as rf (numeral number 5 in FIG. 2), the cross-sectionaleccentricity ratio was calculated from the following formula:

Cross-sectional eccentricity ratio (%)={|Cf−C1|/rf}×100.

(5) Cross-Sectional Flat Ratio

In the same manner as in (4), the cross section of the conjugate fiberwas observed. Among diameters passing through the center of the crosssection, the longest diameter was taken as a major axis A, and theshortest diameter was taken as a minor axis B. The cross-sectional flatratio was calculated according to the following formula:

Cross-sectional flat ratio=major axis A/minor axis B.

(6) Fineness, Strength, Elongation, and Toughness

The fineness, the strength, the elongation, and the toughness weremeasured according to JIS L1013 (2010, chemical fiber filament yarn testmethod). The toughness was calculated according to the followingformula:

(Toughness)=(Strength)×(Elongation)^(0.5).

(7) Uster Unevenness U %

The Uster unevenness U % was measured in a normal mode using USTERTESTER 4-CX manufactured by Zellweger while feeding a yarn at a speed of200 m/min for 5 minutes.

(8) Boiling Water Contraction Ratio and Dry-Heat Contraction Ratio

Ten skeins were produced using a frame measuring device having a framecircumference of 1.0 m, and the boiling water contraction ratio and thedry-heat contraction ratio were calculated according to the followingformula. Both an original length and a length after treatment weremeasured in a state where a load was applied {(notified fineness(dtex)×2)g}. Regarding a contraction treatment, the boiling watercontraction ratio was obtained by immersing in boiling water for 15minutes, and the dry-heat contraction ratio was obtained by treating at200° C. for 5 minutes.

Contraction ratio (%)={(original length (L1)−length after treatment(L2))/original length (L1)}×100.

(9) Number of Fuzz Defects

Using Fly Counter (MFC-120S) manufactured by Toray Engineering Co.,Ltd., 48 conjugate fibers were measured under measurement conditions ofan unraveling speed of 500 m/min and a measuring length of 50000 m, andthe number of detected fuzzes was counted. Based on the counted numberof fuzzes, the following scores were made:

Score 3: The number of fuzzes in all of the 48 fibers: 0

Score 2: The average number of fuzzes of the 48 fibers: less than 0.1,and the maximum number of fuzzes in the 48 fibers: 1

Score 1: The average number of fuzzes of the 48 fibers: 0.1 or more andless than 0.3, and the maximum number of fuzzes in the 48 fibers: 1

Score 0: The average number of fuzzes in the 48 fibers: 0.3 or more, orthe maximum number of fuzzes in the 48 fibers: 2 or more.

(10) High-Order Passability

After the conjugate fiber was warped, the following evaluation scoreswere made according to the number of warping fuzzes detected and thenumber of knitting yarn breakages when knitting was performed at adouble denby structure seam using a tricot knitting machine (36 gauges)including two guide bars using the original yarn obtained for both afront yarn and a back yarn:

Score 3: The number of warping fuzzes: less than 0.3/10 million m, andthe number of knitting yarn breakages: less than 0.5/200 m

Score 2: The number of warping fuzzes: 0.3/10 million m or more and lessthan 0.6/10 million m, and the number of knitting yarn breakages: lessthan 0.5/200 m, or the number of warping fuzzes: less than 0.3/10million m, and the number of knitting yarn breakages: 0.5/200 m or moreand less than 1.0/200 m

Score 1: The number of warping fuzzes: 0.3/10 million m or more and lessthan 0.6/10 million m, and the number of knitting yarn breakages:0.5/200 m or more and less than 1.0/200 m

Score 0: The number of warping fuzzes: 0.6/10 million m or more, or thenumber of knitting yarn breakages: 1.0/200 m or more.

(11) Strength of Fabric After Thermal Adhesion

A tricot fabric was produced by the method of (10), and a heat treatmentwas performed at a melting point of a sheath component+10° C. with a pintenter dryer in a non-loaded state to produce a thermally adheredfabric. The density of the fabric after thermal adhesion was adjusted sothat 66 yarns/2.54 cm (=inch) in a wale direction and 53 yarns/2.54 cm(=inch) in a course direction were set. The strength of the fabric afterthermal adhesion was measured in accordance with JIS 1096: 2010 (testingmethods for woven and knitted fabrics) in a wale (vertical) directionand a course (horizontal) direction, and the following scores were madebased on the strength values:

Score 3: 600 N/5 cm or more in vertical direction and 100 N/5 cm or morein horizontal direction

Score 2: 500 N/5 cm or more and less than 600 N/5 cm in verticaldirection and 100 N/5 cm or more in horizontal direction, or 600 N/5 cmor more in vertical direction, and 80 N/5 cm or more and 100 N/5 cm orless in horizontal direction0

Score 1: 500 N/5 cm or more and less than 600 N/5 cm in verticaldirection, and 80 N/5 cm or more and less than 100 N/5 cm in horizontaldirection

Score 0: less than 500 N/5 cm in vertical direction or less than 80 N/5cm in horizontal direction.

(12) Flow Path Material Water Resistance Test (Salt Removal Rate (%),Water Production Amount (m³/day))

A tricot fabric after thermal adhesion produced in the same manner as in(11) was sandwiched between two RO separation membranes each having athickness of 150 μm, to form a spiral type unit. The spiral type unitwas incorporated into a module having a diameter of 0.2 m and a lengthof 1 m. Sea water having a TDS (soluble evaporation residue) of 3.5% byweight was filtered at a liquid temperature of 25° C. under adifferential pressure of 4.5 MPa for 5 days. The electrical conductivityof the permeation liquid was measured after 5 days, and the removal rateof magnesium sulfate was calculated. The amount of a permeation liquidafter 5 days was measured, and a water production amount per day wascalculated. Based on the results of the test, the following evaluationscores were made:

Score 3: The removal rate of magnesium sulfate: 99.8% or more, and thewater production amount: 45 m³/day or more

Score 2: The removal rate of magnesium sulfate: 99.8% or more, and thewater production amount: 40 m³/day or more and less than 45 m³/day, orthe removal ratio of magnesium sulfate: 99.0% or more and less than99.8%, and the water production amount: 45 m³/day or more

Score 1: The removal rate of magnesium sulfate: 99.0% or more and lessthan 99.8%, and the water production amount: 40 m³/day or more and lessthan 45 m³/day

Score 0: The removal rate of magnesium sulfate: less than 99.0%, or thewater production amount: less than 40 m³/day.

(13) Decision to Pass or Fail

In the evaluation items in (9) to (12), all items having score 2 or morewas taken as pass, and when having at least one item was score 1 or lesswas taken as fail.

Example 1

There were prepared a homo PET polymer of IV 0.67 not including titaniumoxide (high melting point component, melting point: 255° C.), and acopolymerized PET polymer (low melting point component, melting point:230° C.) obtained by copolymerizing 7.1% by mole of isophthalic acid and4.4% by mole of bisphenol A ethylene oxide adduct as copolymerizationcomponents with respect to total acid components and having a titaniumoxide content of 0.05% by weight and IV of 0.65. The high melting pointcomponent was melted at 285° C. in an extruder, and the low meltingpoint component was melted at 260° C. in the extruder. A spinningtemperature was set to 290° C., and weighing was performed by ameasuring pump. After filtration in a pack, by a spinneret nozzle, thecomponents were discharged in a sheath-core conjugate form having acomposite area ratio of 65:35 to form a concentric sheath-corecross-sectional shape as shown in FIG. 1 (cross-sectional eccentricityratio: 0%, and cross-sectional plat ratio: 1.0). At this time, the highmelting point component was disposed in a core and the low melting pointcomponent was disposed in a sheath.

As a take-up device, a direct spinning method (DSD) which drawing andwinding were consistently performed was adopted, and the dischargedpolymer was taken up by a take-up roll (1st HR) set to a surfacetemperature of 85° C. at a speed of 1728 m/min through a cooling partand a fueling part. The polymer was continuously wound around a heattreatment roll (2nd HR) set at 128° C. at 4489 m/min without being woundonce, and a 2.6-fold stretching was performed. The tensions of thestretched and heat-treated yarns were adjusted with a godet roller (3rdGR, 4th GR) set to 4549 m/min and 4584 m/min. A cheese-shaped packagewas wound at a speed of 4500 m/min and a tension of 0.20 cN/dtex, toobtain a sheath-core conjugate fiber having 56 dtex-24 filaments. Theevaluation results for the obtained fibers were shown in Table 1. Usterunevenness U % was 0.4%; a boiling water contraction ratio was 10.3%;and a dry-heat contraction ratio was 17.2%.

As shown in Table 1, the fiber had an excellent strength and elongation,an excellent toughness, and low original yarn fuzz generation. Theobtained original yarn was used for both a front yarn and a back yarn,and knitting was performed at a double denby structure seam using atricot knitting machine (36 gauges) including two guide bars. The fiberhad less warping fuzz generation, less yarn breakage during knitting,and excellent high-order passability. Furthermore, a fabric strengthafter a thermal adhesion treatment with a pintenter at 240° C. (themelting point of the sheath component+10° C.) was high. When the fabricwas used as a flow path material of a water treatment membrane, the hightemperature heat treatment caused a tricot flow path material to haveexcellent dimensional stability, and could secure a stable waterproduction amount while maintaining membrane performance without causingthe breakage or clogging of the flow path material in continuous use.

Examples 2 to 4 and Comparative Examples 1 to 3

Examples 2 to 4 and Comparative Examples 1 to 3 were the same as Example1 except that the melting points of a core component polyester and asheath component polyester were adjusted as shown in Table 1 such that acopolymerization ratio was changed by using the copolymerizationcomponent used in the sheath component of Example 1, and an appropriatespinning temperature was adopted according to the adjustment. Theevaluation results are as shown in Table 1.

Example 5

Example 5 was the same as Example 1 except that a DSD for a spinningmachine was changed to a two-step method, and a spinning condition andthe like was incidentally adjusted. The evaluation results are as shownin Table 1.

Examples 6 and 7

Examples 6 to 7 were the same as Example 1 except that the dischargehole shape of a spinneret was changed, and a cross-sectional shape andthe eccentricity ratio of a core-sheath were changed as shown in Table2. The evaluation results are as shown in Table 2.

Examples 8 to 11

Examples 8 to 11 were the same as Example 1 except that the fineness ofa conjugate fiber and the number of filaments were changed as shown inTable 2. The evaluation results are as shown in Table 2.

Examples 12 to 14

Examples 12 to 14 were the same as Example 1 except that the amounts oftitanium oxide added to a core component polyester and a sheathcomponent polyester were changed as shown in Table 3. The evaluationresults are as shown in Table 3.

Examples 15 to 17

Examples 15 to 17 were the same as Example 1 except that the dischargeamounts of a core component polyester and a sheath component polyesterwere changed, and the ratio of a core-sheath was as shown in Table 3.The evaluation results are as shown in Table 3.

TABLE 1 Unit Example 1 Example 2 Example 3 Example 4 Spinning Productionmethod — DSD DSD DSD DSD condition Spinning temperature ° C. 290 285 280295 Spinneret surface temperature ° C. 281 278 273 287 Raw material Corecomponent melting point ° C. 255 250 250 255 polymer Core componentsoftening ° C. 253 247 247 253 temperature Core component polymer — PETCoPET CoPET PET Sheath component melting point ° C. 230 220 215 235Sheath component softening ° C. 227 215 208 232 temperature Sheathcomponent polymer — CoPET CoPET CoPET CoPET Melting point difference of° C. 25 30 35 20 core and sheath Conjugate fiber IV — 0.65 0.64 0.630.65 Fiber physical Strength cN/dtex 4.0 3.9 3.8 4.0 propertiesElongation % 40 41 38 36 Toughness — 25 25 23 24 Evaluation Number offuzz defects Score 3 3 2 2 Higher-order passability Score 3 3 2 2Strength of fabric after Score 3 3 3 2 thermal adhesion Flow pathmaterial water Score 3 3 3 2 resistance test Comparative ComparativeComparative Unit Example 1 Example 2 Example 3 Example 5 SpinningProduction method — DSD DSD DSD Two-step condition method Spinningtemperature ° C. 275 290 280 286 Spinneret surface temperature ° C. 267281 273 285 Raw material Core component melting point ° C. 245 255 255255 polymer Core component softening ° C. 239 253 253 253 temperatureCore component polymer — CoPET PET PET PET Sheath component meltingpoint ° C. 215 245 210 230 Sheath component softening ° C. 208 239 200227 temperature Sheath component polymer — CoPET CoPET CoPET CoPETMelting point difference of ° C. 30 10 45 25 core and sheath Conjugatefiber IV — 0.53 0.75 0.60 0.66 Fiber physical Strength cN/dtex 3.5 4.13.6 4.1 properties Elongation % 39 40 36 44 Toughness — 22 26 22 27Evaluation Number of fuzz defects Score 1 3 2 3 Higher-order passabilityScore 1 3 1 3 Strength of fabric after Score 1 0 1 3 thermal adhesionFlow path material water Score 1 — 2 3 resistance test

TABLE 2 Unit Example 6 Example 7 Example 8 Example 9 Example 10 Example11 Raw material Core component melting point ° C. 255 255 255 255 255255 polymer Core component softening ° C. 253 253 253 253 253 253temperature Sheath component melting point ° C. 230 230 230 230 230 230Sheath component softening ° C. 227 227 227 227 227 227 temperatureMelting point difference of ° C. 25 25 25 25 25 25 core and sheathConjugate fiber Core-sheath eccentricity ratio % 1.0 5.0 0 0 0 0Cross-sectional flat ratio — 1.0 1.1 1.0 1.0 1.0 1.0 Total fineness dtex56 56 33 44 84 96 Number of filaments — 24 24 24 24 36 24 Single yarnfineness dtex 2.3 2.3 1.4 1.8 2.3 4.0 Fiber physical Strength cN/dtex4.0 3.9 3.8 4.0 4.1 4.1 properties Elongation % 39 38 39 38 40 40Toughness — 25 24 24 25 26 26 Effect Number of fuzz defects Score 3 2 22 3 3 Higher-order passability Score 3 2 2 2 3 3 Strength of fabricafter Score 3 3 2 3 3 3 thermal adhesion Flow path material water Score3 2 2 2 3 2 resistance test

TABLE 3 Unit Example 12 Example 13 Example 14 Example 15 Example 16Example 17 Raw material Core component melting point ° C. 255 255 255255 255 255 polymer Core component softening ° C. 253 253 253 253 253253 temperature Sheath component melting point ° C. 230 230 230 230 230230 Sheath component softening ° C. 227 227 227 227 227 227 temperatureMelting point difference of ° C. 25 25 25 25 25 25 core and sheathAmount of titanium oxide of wt % 0 0.3 2.0 0 0 0 core component Amountof titanium oxide of wt % 0 0.3 2.0 0.05 0.05 0.05 sheath componentConjugate fiber Core-sheath ratio — 65:35 65:35 65:35 75:25 55:45 80:20Fiber physical Strength cN/dtex 4.0 4.0 3.8 4.1 4.0 4.1 propertiesElongation % 38 39 40 40 40 42 Toughness — 25 25 24 26 25 27 EvaluationNumber of fuzz defects Score 2 3 2 3 3 3 Higher-order passability Score2 3 2 3 2 3 Strength of fabric after Score 3 3 2 2 2 2 thermal adhesionFlow path material water Score 3 3 2 2 2 2 resistance test

1-3. (canceled)
 4. A thermally adhesive sheath-core conjugate fibercomprising: a core part including a polyester having a melting point of250° C. or higher; and a sheath part including a polyester having amelting point of 215° C. or higher and lower by 20 to 35° C. than thatof the polyester constituting the core part, wherein the thermallyadhesive sheath-core conjugate fiber has a strength of 3.8 cN/dtex ormore and an elongation of 35% or more.
 5. The thermally adhesivesheath-core conjugate fiber according to claim 4, wherein thesheath-core conjugate fiber has a total fineness of 30 dtex or more anda single yarn fineness of 3.0 dtex or less.
 6. A tricot fabriccomprising the thermally adhesive sheath-core conjugate fiber accordingto claim
 4. 7. A tricot fabric comprising the thermally adhesivesheath-core conjugate fiber according to claim 5.